在常温下，将下列物质投入足量稀盐酸中，能产生气体且有金属不溶物残留的是（  ）

下列说法不正确的是（   ）

看图填数。

____个十

根据短文内容, 回答下列问题。
    I am Helen. I study in the No.1 Middle School now. There are forty-five students in my class. All of the students like to travel(旅游). Eight students like to travel by plane, because they think it is fast. It only takes about two hours to travel by plane from Beijing to Shanghai. But some students think taking a plane is too expensive. Twenty-two students usually travel by train. The trains are very fast, but they are cheaper (更便宜). And they can see interesting things through the windows. Fifteen students love to travel by car. Their parents drive them to some beautiful places. They can have a good time with the family. Do you know how I like to travel? I'm one of the twenty-two students.

设复数a+bi（a，b∈R）的模为 $\sqrt{3}$ ，则（a+bi）（a﹣bi）=____．